| English | 의미 |
|---|---|
| externality/ekˈstɜːnælɪti/ | 외부성 |
| negative externality/ˈneɡətɪv ekˈstɜːnælɪti/ | 부정적 외부성 |
| third party/θɜːd ˈpɑːti/ | 제3자 |
| marginal private cost/ˈmɑːdʒɪnl ˈpraɪvət kɒst/ | 사적 한계 비용 |
| overproduces/ˌəʊvəprəˈdjuːsɪz/ | 과잉 생산 |
| positive externality/ˈpɒzɪtɪv ekˈstɜːnælɪti/ | 긍정적 외부성 |
| marginal private benefit/ˈmɑːdʒɪnl ˈpraɪvət ˈbenɪfɪt/ | 사적 한계 수익 |
| underproduces/ˌʌndəprəˈdjuːsɪz/ | 생산 부족 |
| Pigouvian tax/pɪˈɡuːvɪən tæks/ | 피구비세 |
| subsidy/ˈsʌbsɪdi/ | 보조금 |
| tradable permits/ˈtreɪdəbl ˈpɜːmɪts/ | 거래 가능 허가증 |
The cost you don't pay
- A factory's smoke drifts over a neighbourhood the owner never meets.
- A vaccine protects not just you, but everyone you don't infect.
- These spillovers land on people outside the deal — and the market ignores them.
- Each one is an externality 外部性, and it makes the market produce the wrong amount.
An externality is a cost or benefit that falls on:
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The spillover lands on someone outside the buyer-seller deal.
Negative and positive externalities
- A negative externality 负外部性 (pollution) imposes a cost on a third party 第三方. Marginal social cost sits above the marginal private cost 边际私人成本, so the market overproduces 过度生产.
- A positive externality 正外部性 (vaccination) gives others a benefit. Marginal social benefit sits above the marginal private benefit 边际私人收益, so the market underproduces 生产不足.
An externality
A negative externality puts social cost above private cost, so the market overproduces. A tax equal to the external cost restores the efficient quantity.
A good with a negative externality (like pollution) is:
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The firm ignores the extra social cost, so it makes more than the efficient quantity.
A good with a positive externality (like vaccination) is underproduced by the market.
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Buyers ignore the benefit to others, so the market makes too little.
How governments correct them
- A Pigouvian tax 庇古税 equal to the external cost raises the polluter's private cost to the social cost, cutting output to the efficient level.
- A subsidy 补贴 equal to the external benefit encourages more of a good thing (like education).
- Tradable permits 可交易许可证 cap total pollution and let firms trade the right to pollute, so cuts happen where they are cheapest.
A tax set equal to the external cost of pollution is called a ______ tax.
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A Pigouvian tax internalises the externality, cutting output to the efficient level.
Select all tools a government can use to correct externalities.
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Taxes, subsidies and permits all make people face the full social cost or benefit.
A worked case
- A factory's private cost of a tonne of steel is 200, but its smoke does 30 of harm to residents.
- So the true social cost is $200 + 30 = 230$; left alone, the factory ignores the 30 and overproduces.
- A Pigouvian tax of exactly 30 makes the factory pay the full 230.
- The tax "internalises" the externality, cutting output to the efficient amount.
A tonne of steel has a private cost of 200 and does 30 of harm to others. What per-tonne Pigouvian tax makes the firm face the full social cost?
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The tax equals the external cost, 30, so the firm pays the full social cost of 230.
An externality spills a cost or benefit onto a third party. A negative one (social cost above private) causes overproduction; a positive one (social benefit above private) causes underproduction. Governments fix them with a Pigouvian tax, a subsidy, or tradable permits.